The read-only optical recording media such as a CD (Compact Disk), DVD (Digital Versatile Disk), etc. are well known as information recording media to which information such as copyrighted music and video works can be recorded via modulation. Read-only recording media to which content such as a music work, video work or the like is recorded should be warranted for no difference in quality from one medium to another. This warranty is achieved by forming first a single master and replicating read-only recording media one after another on the basis of the single master.
Especially, a large number of disk-shaped read-only optical recording media each having recorded therein, as a pit-and-pit pattern on a substrate, a digital signal resulted from conversion of the same content information, such as a CD or DVD, can be produced at a time by replicating a single master. Therefore, the disk-shaped read-only optical recording medium is more advantageous in less deterioration of the master during replication, considerably easier replication, shorter time for replication and lower cost than the other recording media using a rewritable recording medium as a read-only recording medium, such as a tape cassette and video tape cassette for video tape recorders.
On the other hand, it is not always desirable in light of the medium management that only the same information can be written to all media, which is because the media cannot be distinguished from each other. The “medium management” is originally required for the quality control at the side of the medium manufacturer. However, since distribution of CDs and DVDs copied with no legitimate right has recently become a serious problem, the medium management has become more and more important for management of read-only recording media against illegal copying as well as for management of the copyright on the content of the medium.
The problem in the medium management against illegal copying lies in that no distinction can be made between a genuine medium and illegal copy of the medium because of the aforementioned characteristic of the read-only recording medium.
To solve the above problem, there has been proposed to record unique information unique to each of read-only recording media. An illegal copy of a recording medium having recorded therein unique information, namely, information different from one to another medium, will carry no such unique information or will not successfully be played. Therefore, this measure will be very effective for prevention of illegal copying or the like.
For the above reason, it is necessary to record unique information to each of the read-only recording media before shipment. For this purpose, an information recording method for this recording of unique information is necessary.
For recording unique information to each of read-only recording media, it is known to mark or attach a bar code carrying the unique information on the surface or like of the read-only recording medium. However, the bar code is easy to forge and is recorded separately from a part of the medium where information such as content is recorded. Therefore, a more effective method than the bar code recording has been demanded.
For postscription of identification information to the medium part where information such as a content is recorded, there has been proposed a medium management method using the Postscribed ID (trademark) developed by the SONY DISC TECHNOLOGY etc.
The method developed by the SONY DISC TECHNOLOGY is such that a large number of optical recording media such as a CD is produced once, by a stamper, from a material that can be melted with postscribing light to form a reflecting layer as a recording layer, and then a predetermined portion (land) of a pit-land-pit pattern formed on a recording track on each of optical recording media is irradiated with high-power laser light to pit the predetermined land portion.
More specifically, with such a land portion to be pitted being set in a plurality of places on the read-only recording medium, it is judged based on information unique to the recording medium whether each of such land portions should be pitted or left as the land, and each land portion is irradiated with laser light on the basis of the result of judgment, to thereby postscribe unique identification information at a part of the recording medium where actual information such as a content or the like is recorded.
The existence of the above-mentioned bar code on the recording medium is visually known. Since the medium-unique information written on the recording medium as above cannot visually be known, however, the recording medium thus produced by the method proposed by the SONY DISC TECHNOLOGY is not easily forgeable. Also, since the medium-unique information is recorded on the recording track, any special reading system is not necessary. Therefore, different from the appending of medium-unique identification information as a bar code, the medium management proposed by the SONY DISC TECHNOLOGY is suitable for the quality control as well as for the information management etc.
However, since the recording medium playing apparatus should detect where the identification signal is recorded, the land portion to be pitted has to be predetermined on the recording medium and a data row, if any, formed not in compliance with the modulation rule after the land portion is pitted will make it impossible to play back the recording medium.
Recording rules used in conjunction with the EFM (Eight-Fourteen Modulation) technique or the EFM plus modulation technique normally adopted in the CD and DVD to solve the above problems of the related art are proposed in the Japanese Patent Laid Open Nos. 2003-141742 and -151145.